"Apologia" means "explanation". In this case, a Greek philosopher who converted to Christianity attempts to explain to Emperor Marcus Aurelius why Christianity is a good thing; or failing that, what Christians believe and do as opposed to what is rumored; and why it was bad for the Empire to persecute Christians just for holding Christian beliefs. The apologia is circa 147-161 A.D.
If you're interested at all in history, politics, or religion, this is like a trip in a time machine.
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